This invention relates to an improved fermentation medium and process for making an aliphatic polycarboxylic acid using said medium.
Long-chain alpha, omega-dicarboxylic acids, i.e., those having a carbon number of 9 or higher, are used as raw materials in the synthesis of a variety of chemical products and polymers.
Diacids with carbon numbers greater than four are currently produced almost exclusively by nonbiological conversion processes. These types of chemical processes for the production of diacids have a number of limitations and disadvantages. Each process is restricted to the production of diacids of specific carbon chain lengths, based on the starting material used. For example, the dodecandioic acid process begins with butadiene, therefore the products of this reaction process are limited to acids with chain lengths in multiples of four. In addition, the processes are based on nonrenewable petrochemical feedstocks, and the multireaction conversion process produces unwanted byproducts which result in yield losses, heavy metal wastes, and nitrogen oxides which must be destroyed in a reduction furnace.
Biological conversion processes for the production of diacids have a number of potential advantages relative to the existing non-biological conversion processes. Primary among these is the use of renewable feedstocks as starting materials and the ability to produce the diacid without the generation of hazardous chemical byproducts which necessitate costly waste disposal processes.
Another important advantage achieved by using a biological process is that such a process can easily be adapted to produce a wide variety of diacids using the same biocatalyst and the same equipment. Because current organic chemical syntheses are suited to the production of only a single diacid, the synthesis of several different diacids would require the development of a new synthetic scheme for each diacid. On the other hand, a yeast biocatalyst can be used to produce diacids of varying lengths using the same equipment, media and protocols merely by providing a different substrate to the yeast.
U.S. Pat. No. 6,004,784, the entire contents of which is hereby incorporated by reference, discloses a semi-synthetic fermentation medium which employs corn steep liquor and brewers yeast extract in order to reduce the cost of conventional fermentation media which contain expensive, highly standardized yeast extracts and yeast nitrogen bases.
The problem associated with the use of such inexpensive substitutes is many fold. They result in a fermentation broth having significant odor emissions when sparged with air. Particulate matter, especially combined with high levels of bacteria, contained in corn steep liquor and crude yeast extracts make them difficult to sterilize and contribute to the bioburden on media sterilization equipment. These substitutes also contain many unmetabolizable components that contribute to color and color stability problems which need to be attended to using additional purification steps with their incumbent product losses. The selection of these substitutes, while lowering media cost, add additional process costs. Consequently, there remains a need for a low-cost, biofermentation medium which provides nutrients to support growth of the yeast biocatalysts permitting high specific productivity of polycarboxylic acids, polyols, and polyhydroxy acids.
Although long chain dicarboxylic acids have limited solubility in water in their undissociated or partial salt form, there are many cases where it is necessary to handle them in an aqueous medium. Examples include fermentation and recovery processes used to produce dicarboxylic acids, interfacial polymerization reactions, emulsion polymerization reactions, and enzymatic reactions.
Aqueous suspensions of long chain dicarboxylic acids tend to be highly viscous and are therefore difficult to handle. Major operational issues in fermentation reactions used to prepare dicarboxylic acids include oxygen transfer, heat transfer, gas hold-up in the fermentation broth, and broth hold-up in the exiting gas (foaming) each being affected by the Theological characteristics of the broth. Likewise, in filtration processes used to recover dicarboxylic acids from the fermentation broth, high viscosity leads to impractical filtration rates. In polymerization and enzyme reactions, viscosity effects on mass transfer would be a major issue since it is desirable to have rapid, predictable contact of reagents.
In DE 29 09 420 A1, Watanabe, et al. describes a method for treating suspensions of long-chain dicarboxylic acids in cell-free fermentation broth to improve filtration rates and purity of recovered diacids. He demonstrated that by heating the aqueous dicarboxylic acid suspension at pH 4 or below to above 50xc2x0 C. for 1 hour or more, he could control the particle size distribution and particle morphology. He describes that by growing the particles to an average particle size of 40-50 xcexcm he could obtain improved filtration rates, lower filter cake moisture, and higher dicarboxylic acid purity in the filter cake. Unfortunately, this method has limited utility for many applications where aqueous suspensions of long chain dicarboxylic acids are encountered.
Many fermentation and enzyme reactions occur over a broader pH range and below 50xc2x0 C. In many cases, enzyme and microbial activity would be reduced or destroyed under the conditions described by Watanabe, et al. Interfacial and emulsion polymerization reactions involving aqueous dicarboxylic acid suspensions could only be limited to thermally stable reagents. There is therefore a need for alternative methods of controlling rheological properties of aqueous suspensions of long chain dicarboxylic acids.
In one aspect, the present invention is directed to a fermentation medium and process for making polycarboxylic acids, polyols, and polyhydroxy acids using said medium. The fermentation medium contains:
(a) a source of metabolizable carbon and energy;
(b) a source of inorganic nitrogen;
(c) a source of phosphate;
(d) at least one metal selected from the group consisting of alkali metals, alkaline earth metals, transition metals, and mixtures thereof; and
(e) a source of biotin, substantially free of particulate matter and bacteria.
The present invention is also directed to a process for making polycarboxylic acids, polyols and polyhydroxy acids involving:
(a) providing an organism capable of producing a polycarboxylic acid, a polyol or a polyhydroxy acid;
(b) providing a substrate capable of being converted into a polycarboxylic acid, a polyol or a polyhydroxy acid by the organism;
(c) providing a fermentation medium containing:
(i) a source of metabolizable carbon and energy;
(ii) a source of inorganic nitrogen;
(iii) a source of phosphate;
(iv) at least one metal selected from the group consisting of alkali metals, alkaline earth metals, transition metals, and mixtures thereof; and
(v) a source of biotin, substantially free of particulate matter and bacteria; and
(d) fermenting the organism in the fermentation medium.
The present invention also relates to an aqueous suspension containing at least one dicarboxylic acid which also includes water, and a fatty material in an amount effective to cause formation of substantially disk shaped, substantially partially spherical shaped or substantially spherical shaped dicarboxylic acid particles.
The present invention also relates to a method for modifying the rheological properties of an aqueous suspension containing a dicarboxylic acid including adding an effective dicarboxylic acid particle shape forming amount of fatty material to the suspension to cause formation of shaped dicarboxylic acid particles, wherein the shape is selected from the group consisting of substantially disk shaped, substantially partially spherical shaped and substantially spherical shaped.